D-chiro-Inositol and myo-inositol, which have respectively the structural formulae ##STR1## occur naturally, with the more abundant myo-isomer being generally found in plants as its hexaphosphate, phytic acid, or as salts of the hexaphosphate, phytin. In mammals, the mono- and polyphosphate forms of these compounds are components of cellular membranes and can function as insulin mediators. Following the observation that the conversion of myo- to chiro-inositol is deficient in mammals suffering from certain types of diabetes, it has been proposed more recently that supplementing the diet with D-chiro-inositol can help control blood glucose levels of patients affected by this disease.
The need for investigational and commercial quantities of D-chiro-inositol has led to the development of several methods for the isolation (by extraction from plant tissues), partial synthesis or complete synthesis of that compound. Especially promising is hydrolysis of the aminoglycoside kasugamycin (produced by fermentation of Streptomyces kasugaspinus) as described in U.S. Pat. No. 5,091,596 issued to Kennington et al. According to that patent, kasugamycin is treated with trifluoroacetic acid for 3 hours at 100.degree. C., after which the resulting D-chiro-inositol is isolated by resin and gel chromatography and purified by recrystallization from 90% ethanol. Alternatively, kasugamycin may be treated with hydrochloric acid for 8 hours at 90.degree. C., followed by isolation of the D-chiro-inositol by resin chromatography and subsequent purification.
However, when preparing larger amounts of product, a relative drawback of each of the above acid hydrolysis procedures is the expense of the chromatographic isolation step in which D-chiro-inositol is purified. Similarly, the isolation of D-chiro-inositol product from dilute aqueous solution, as by lyophilization, may be unduly time-consuming when carried out as a part of an industrial process. Consequently, there remains a need for more efficient methods whereby high-purity D-chiro-inositol can be prepared, economically and on a large scale, from kasugamycin.